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An internal-and-external-cavity Fabry–Perot interferometer (IECFPI) model was mathematically constructed. Based on the IECFPI configuration, a crosstalk-free fiber optic sensor for simultaneous measurement of refractive index (RI) and temperature was proposed and experimentally demonstrated. The internal cavity was a silica cavity, while the external one consisted of an open cavity and silica cavity. The open cavity was formed by an offset single-mode fiber (SMF) sandwiched between two sections of SMF, and the silica cavity was formed by a well-cleaved SMF. A sensitivity coefficient (SC) matrix of the proposed sensor was used to determine the RI and temperature by monitoring the wavelength shifts of the envelope and fine fringes. The proposed sensor can be used for simultaneous measurement of RI and temperature based on the inverse of the SC matrix. Experimental results demonstrated that the RI sensitivities for the envelope and fine fringes were 1084.9 and 124.2 nm/RIU, respectively. Temperature sensitivities of 3.5 and 9.8 pm/°C were also achieved for the envelope and fine fringes, respectively. The crosstalk between the RI and temperature was thus eliminated. In addition, the proposed sensor has a compact size, simple fabrication, and an all-fiber structure, making it a potential candidate for many applications, such as the food industry and environment monitoring.

Laser-ultrasonic excitation holds promising prospects in nondestructive testing and structural health monitoring. This paper proposes a multipoint, energy-equal laser-ultrasonic actuator based on multiple peanut-shape (PNS) structures in a single mode fiber link. The PNS structures were fabricated by fiber micro-matching operations using a fiber splicer. The PNSs effectively couple the laser energy from the core mode into the cladding modes in the fiber. Moreover, the coupling ratio can be adjusted by controlling the taper diameter of the PNSs. For energy control, multiple PNS structures are fabricated and connected in order from small to large coupling ratios. Experiments were performed on an actuator with four PNSs of different taper diameters (138.71 $\mu \text{m}$ , 143.42 $\mu \text{m}$ , 158.23 $\mu \text{m}$ , and 180.19 $\mu \text{m}$ ) distributed along a single fiber. With its simple structure, energy control, and multipoint functionality, this all-fiber laser-ultrasonic actuator shows great potential in future multipoint ultrasound applications.

A femtosecond soliton erbium-doped fiber ring laser with the symmetrical saturable absorber (SA) of graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) is proposed and proved. Based on the nonlinear multimode interference (NL-MMI) effect of SA, the fiber laser achieved femtosecond soliton mode-locking operation and repetition rate tuning. The duration of soliton was 364 fs at 1562.5 nm and repetition rate was tunable from 10.29 MHz to 763.36 MHz. In the structure of SA, a short step index multimode fiber (SIMF) was inserted between two graded index multimode fibers (GIMFs) to generate more high-order modes, adjust the self-focusing length, and improve operation stability of mode-locked fiber laser. The SA also has the advantages of immunity to the external environment variation, high damage threshold and inoxidizability, which make the laser operate stably for a long time.

A high-sensitivity fiber-optic strain sensor, based on the Vernier effect and separated Fabry–Perot interferometers (FPIs), is proposed and experimentally demonstrated. One air-cavity FPI is used as a sensing FPI (SFPI) and another is used as a matched FPI (MFPI) to generate the Vernier effect. The two FPIs are connected by a fiber link but separated by a long section of single-mode fiber (SMF). The SFPI is fabricated by splicing a section of microfiber between two SMFs with a large lateral offset, and the MFPI is formed by a section of hollow-core fiber sandwiched between two SMFs. By using the Vernier effect, the strain sensitivity of the proposed sensor reaches $\text{1.15 nm/}\mu \varepsilon $ , which is the highest strain sensitivity of an FPI-based sensor reported so far. Owing to the separated structure of the proposed sensor, the MFPI can be isolated from the SFPI and the detection environment. Therefore, the MFPI is not affected by external physical quantities (such as strain and temperature) and thus has a very low temperature cross-sensitivity. The experimental results show that a low-temperature cross-sensitivity of $\text{0.056 } \mu \varepsilon /^ {\circ }{\text{C}}$ can be obtained with the proposed sensor. With its advantages of simple fabrication, high strain sensitivity, and low-temperature cross-sensitivity, the proposed sensor has great application prospects in several fields.

We theoretically and experimentally demonstrate an all-fiber multi-channel ultrasonic sensor using a switchable fiber Bragg gratings (FBGs) filter in an erbium-doped fiber laser (EDFL). The FBGs are not only used as the filter to determine the laser wavelength, but also as the sensing element to induce the intensity response of the lasing line via cavity loss modulation from the ultrasound-induced relative spectral shift of the matched FBGs. The switchable FBGs filter consists of a tuning FBG and several sensing FBGs. Multi-channel ultrasound detection is achieved via this filter by tuning an FBG to scan the spectra of multiple sensing FBGs. The ultrasonic-detection channel can be flexibly and efficiently switched via tuning the tunable FBG to match with any one of the sensing FBGs. A novel dynamic response model of the EDFL based on wavelength-dependent gain is proposed and developed to study the effects of different spectrally matched FBG positions and the consistency of the ultrasound response of each detection channel. The theoretical results show that the optimal sensing position is at the overlapping regions of spectra when the slope of the FBGs is greatest and the laser power is relatively high. Meanwhile, the consistency of the ultrasound response for each detection channel is influenced by the laser-resonance condition of the EDFL and can be optimized by adjusting the laser-cavity loss. Such theoretical results are well-verified experimentally. This sensor-laser-integrated system achieves high ultrasonic detection response since cavity-loss modulation is related to the amplifying effect of the laser. Using this method, an eight-channel switchable ultrasonic-sensing system has been demonstrated, covering nearly a 16-nm spectral range. By further controlling the cavity loss in the laser system, the consistency of ultrasonic response of each detection channel was optimized. The proposed all-fiber system has multiple- detection channels in a single laser system and consistent ultrasonic-detection response at each channel; it shows great potential for fiber-optic-ultrasonic-detection applications.

We propose and demonstrate a multi-point, self-adaptive fiber ultrasonic sensor based on fiber Bragg gratings (FBGs). The sensor is constructed from matched FBG pairs (FBGPs) and a tunable optical filter in a fiber ring laser. FBGPs with different Bragg wavelengths are used as both the comb filter to produce potential lasing lines and the ultrasonic sensing elements. The ultrasonic signal is directly detected by monitoring the intensity response at each laser channel to the cold-cavity loss modulation from the spectral shift of matched FBGPs. The laser channel between the FBGPs is actively switched using the tunable optical filter, thereby achieving multi-point and switchable detection yet avoiding mode competition in the lasers. Meanwhile, to achieve self-adaptability, the two FBGs of the FBGP are fixed side by side at the same location of the structure such that both FBGs respond similarly to static strain and temperature variation. The multi-point system is promising for the robustness in the practical applications because it is insensitive to static strain ranging over 1400 μ ϵ and temperature variation from 20 °C to 50 °C, respectively.

A photo-invertible helical cholesteric superstructure was constructed by doping a novel chiral fluorescence photoswitch and a static dopant with opposite handedness into a nematic host. The handedness of circularly polarized luminescence can be reversibly inverted accompanied by a positive-negative change of luminescence dissymmetry factor values upon alternate light irradiations.

A severe infectious disease characterized by nephritis, hepatitis and splenitis has attacked goslings around Shandong province in China since 2016. A novel chicken-origin avian orthoreovirus (ARV) was isolated with LMH cells from affected goslings named Reo/Goose/SDPY/1116/17 (SDPY-ARV) strain, and the infection was successfully reproduced experimentally. The ARV-SDPY full genome sequencing was conducted using Next-Generation Sequencing (NGS) technique on Illumina HiSeq platform. The complete genome of SDPY-ARV was 23,427 bp in length and consist of 10 dsRNA segments ranged from 1192 bp (S4) to 3958 bp (L1) which encoding 12 viral proteins. Genomic sequence analysis showed that the SDPY-ARV strain is in the same branch with broiler, pheasant-origin ARV isolates, and shares 51.8–96.2% of nucleotide identity of σC gene with them; while only 49.3–50.3% with waterfowl isolates. In addition, the occurrence of 10 segments genetic reassortment of SDPY strain is confirmed among the PA15511, the 1733 and the PA13649 strains from America. In conclusion, the causative agent of gosling hemorrhagic necrotic hepatitis and nephritis occurring in China is a novel chicken-origin goose orthoreovirus.

In this study, we propose and demonstrate a multipoint fiber-optic laser-ultrasound transducer based on fiber waist-enlarged tapers (WETs), which are fabricated by taper fusing two single-mode fibers. The WET structure can effectively extract some of the light energy from the fiber core and transfer it to the cladding to form a series of higher-order modes that can be used to excite ultrasound waves. The light energy in the cladding can be absorbed and converted into ultrasound waves by the photoacoustic composite coating on the fiber near WET. The coupling efficiency of the WET is dependent upon its taper length and, therefore, can be easily controlled by the splicer during fabrication. Thus, by controlling coupling efficiencies of the WETs, a multipoint laser-ultrasound actuator with a balanced signal strength can be obtained. We constructed a prototype of the actuator and successfully generated ultrasound waves with balanced strengths at four points by connecting four WETs with coupling ratios of 25.24%, 32.25%, 49.52%, and 90.62% in a fiber link. This multipoint laser-ultrasound actuator is simple to fabricate and provides a balanced ultrasonic signal strength, and thus, has various potential applications in fiber-optic active ultrasound testing technologies.

A wavelength tunable, dark pulse, and bright pulse-switched dual-wavelength fiber ring laser is reported. Through adding high nonlinear optical fiber as a nonlinear medium in the fiber ring cavity, the double-wavelength dark-bright pulse pair can be formed. The separation of dark-bright pulse pair can be achieved by polarization beam splitter. The dark pulse and bright pulse with orthogonal polarization correspond to different wavelengths, respectively. Then, via tunable optical filter and polarization controller to filter out the wavelength we need and adjust the polarization, we achieved the interconversion of dark pulse and bright pulse in the same wavelength and the tunableness of wavelengths of dark pulse and bright pulse in our laser.

In 2017, an emerging disease outbreak with high mortality in goslings occurred in China. A novel goose astrovirus was isolated and identified as the causative agent of this disease. Genomic analysis revealed that this virus strain was significantly distinct from published astrovirus strains.

A severe infectious disease characterized with gout, haemorrhage and swellings of kidneys has affected goslings around the major goose-producing regions in China since November 2016. A Novel goose-origin astrovirus (AStV), designated as AStV/SDPY/Goose/1116/17 (AStV-SDPY) strain, was isolated from diseased goslings, and experimental reproduction of gout was successful using the AStV-SDPY strain. Additionally, the AStV-SDPY was conducted for its full genome sequencing characterization using next-generation sequencing (NGS) technique on Illumina HiSeq platform. A complete genome of the AStV-SDPY was 7,252 nt in length and encoded three viral proteins. Phylogenetic analysis revealed that AStV-SDPY strain belongs to an independent branch of avian astroviruses, and the nucleotide homology among AStV-SDPY and other classic avian astrovirus strains was only 48.8%-68.2%. Results of above data indicated the causative agent of the gosling gout occurring in China is a novel divergent goose astrovirus.

A high sensitivity humidity fiber sensor based on all-agar Fabry–Perot (FP) interferometer is proposed and experimentally demonstrated. The sensor is fabricated by filming a thin layer of moisture-sensitive agar to single mode fiber with end dipping method. Due to the all-agar FP cavity structure, both the size and the RI changes of agar film in the swelling effect are fully utilized to induce the frequency shift, the sensor exhibits a high sensitivity of 4.20 nm/%RH, with relative humidity (RH) ranging from 25%RH to 95%RH at 25 °C. Moreover, owing to the short FP cavity, $7.10~\mu \text{m}$ , the proposed sensor provides a short response time less than 340 ms with the humidity level changed from 64.0%RH to 74.2%RH. The proposed sensor also exhibits other superior performances in terms of good stability, low cost, and easy fabrication. Such good characteristics make the proposed sensor a good candidate for practical applications.

A high-sensitivity Fabry–Perot interferometer (FPI) strain sensor based on a concave-core photonic crystal fiber (CPCF) was proposed and demonstrated. The FPI was formed by directly splicing a CPCF to a standard single-mode fiber. The CPCF was fabricated by cleaving a high-numerical-aperture solid-core photonic crystal fiber under axial tension using a traditional fiber cleaver. An FPI strain sensor with a cavity length of 4.85 μ m and a strain sensitivity of 31.58 pm/ μ ϵ was successfully produced. The sensor also demonstrated a low temperature sensitivity of 0.653 pm/°C, reducing the cross-sensitivity between tensile strain and temperature. The benefits of the proposed sensor include simple fabrication, high strain sensitivity, and low temperature cross-sensitivity, making it attractive for practical applications.

We propose and demonstrate a fiber sensor for simultaneous temperature and strain measurements. The proposed sensor is implemented by a cascaded-cavity Fabry–Perot (FP) fiber interferometer. The two cascaded FP cavities comprise a micro-air-cavity in a hollow-core tube fiber and a micro-silica-cavity in a standard single-mode fiber. To separate the interference spectrum of each FP cavity, the total spectrum is filtered in the frequency domain through band-pass filters, whose central frequencies were predesigned based on the relationship between the spatial frequency and free spectral range of each FP cavity. The different cross-sectional areas and thermal-optic coefficients of the two FP cavities confer different sensitivities to temperature and strain. Both parameters were measured simultaneously by tracking the wavelength shifts in the filtered interference spectra of the FP cavities. Moreover, the temperature–strain cross-sensitivity was compensated by solving a sensitivity-coefficient matrix equation for the two cavities, using the calibrated temperatures and strains. Other advantages of the proposed sensor are simple fabrication and an all-fiber structure. Owing to these properties, the proposed sensor is potentially applicable to real sensing applications.

A switchable and tunable multiwavelength erbium-doped fiber laser is proposed and demonstrated based on a two-stage Lyot filter and intensity-dependent loss (IDL) effect induced by a nonlinear optical loop mirror (NOLM). The proposed laser can achieve multi-parameter individually tuning functions, such as adjusting the channel-spacing, number, and spectral-range of lasing line. The channel spacing can be switched via adjusting the beam's polarization in the Lyot filter among 0.53, 0.78, and 1.56 nm. Meanwhile, the number and the spectral range of the multiwavelength lasing line can be independently controlled by IDL modulation through the combination of adjusting pump power and the birefringence in the loop of the NOLM. The individual tuning method of the proposed laser on each specific output characteristic provides more convenience and practicality to the applications.

We report on the generation of high-order solitons with order continuously adjustable in an erbium-doped fiber laser mode-locked by a graded index multimode fiber–step index multimode fiber–graded index multimode fiber (GIMF–SIMF–GIMF) saturable absorber (SA). The SA has advantages of high damage threshold, easy fabrication and low cost. The fundamental soliton to eleventh-order soliton were obtained by adjusting the pump power and PC. It was found that both increasing pump power and adjusting PC can affect the solitons splitting during experiment. The generation of high-order solitons is due to the peak power clamping effect of laser cavity and the pulse shaping effect of GIMF–SIMF–GIMF SA. Last but not least, this is the first time to adjust the order of solitons continuously from the first to eleventh in a fiber laser mode-locked by GIMF–SIMF–GIMF SA.

A multiwavelength erbium-doped fiber laser based on tunable comb spectral filter and intensity-dependent loss modulation is proposed and experimentally demonstrated. The laser allows fine and multifunctional tunable operations of channel-spacing, peak-location, spectral-range, and wavelength-number. More specifically, channel-spacing switch from 0.4 nm to 0.2 nm and peak-location adjustment within half of free spectrum range are obtained via controlling the tunable comb filter. The wavelength-number and the spectral-range of the lasing lines can be accurately controlled by intensity-dependent loss modulation in the laser cavity, enabled by a power-symmetric nonlinear optical loop mirror. In addition, fine control over the wavelength-number at fixed spectral-range is realized by simply adjusting the pump power. More important, the tunable operation process for every type of specific parameter is individual, without influences for other output parameters. Such features of this fiber laser make it useful and convenient for the practical application.

The bright-dark soliton pair in a passively mode-locked fiber laser based on the topological insulator: Bi2Se3/polyvinyl alcohol (PVA) film in the proper polarization state and the pump power is experimentally demonstrated. By carefully adjusting the pump power and the polarization state, the bright-dark soliton pair could be easily observed. Furthermore, it is found experimentally that the formation of the bright-dark soliton pair is mainly due to the polarization effect based on the high nonlinear effect of topological insulator: Bi2Se3/PVA film. We also demonstrate that the pulse shape of the bright-dark soliton pair can be affected by the total net cavity dispersion in the fiber laser.

A tunable multiwavelength erbium-doped fiber laser (MWEDFL) based on nonlinear optical loop mirror (NOLM) and tunable birefringence fiber filter (BFF) is proposed and demonstrated. By combination of intensity-dependent loss modulation induced by NOLM and pump power adjustment, the proposed laser can achieve independent control over the number of lasing lines, without affecting other important characteristics such as channel spacing and peak location. In addition, the laser allows wavelength tuning with both the peak location and the spectral range of lasing lines controllable. Specifically, the peak location of lasing lines can be controlled to scan the whole spectral range between adjacent channels of comb filter by adjusting the BFF. Moreover, the spectral range of lasing lines can be controlled by adjusting NOLM. This tunable MWEDFL may be useful for fiber-optic communication and fiber-optic sensing.

Multidrug resistance (MDR) is one of the most important obstacles affecting the efficacy of chemotherapy treatments for numerous types of cancer. In the present study, we have demonstrated the possible function of Twist1 in the chemosensitivity of head and neck squamous cell carcinoma (HNSCC) and have identified that its mechanism maybe associated with MDR1/P-gp regulation. To investigate this, the hypopharyngeal cancer cell line, FaDu, and its MDR cell line induced by taxol, FaDu/T, were employed. Stable transfectants targeted to Twist1 overexpression and Twist1 silencing based on FaDu were also conducted. Morphological observation, flow cytometry, reverse transcription-polymerase chain reaction (RT-PCR), western blotting and laser scanning confocal microscope detection were utilized to detect the associations between Twist1 and the chemosensitivity of FaDu cells. Our results demonstrated that Twist1 and MDR1/P-gp were upregulated in FaDu/T cells in a MDR dose-dependent manner. The anti-apoptotic capabilities of FaDu/T cells were enhanced during MDR progression, with apoptosis-related proteins (Bcl-2, Bax, activated caspase-3 and caspase-9) changing to resist apoptosis. Twist1 overexpression decreased the sensitivity of cells to taxol as revealed by a significant increase in MDR1/P-gp and IC50 (P

We report a high-temperature fiber-optic sensor based on measuring the spectral fringes of a Fabry-Perot (FP) cavity on a microstructure fiber (MF) when the gas pressure in the cavity is varied through the holes in the MF. Theoretical analysis shows that the absolute temperature can be deduced from the slope of the spectral shift versus pressure curve, which requires no calibration and is insensitive to the FP cavity length variations. For demonstration, we fabricated a miniature sensor whose FP cavity is formed by sandwiching a fuse-silica tube between a side-hole MF and a solid-core fiber. Using the holes in the MF as gas channels, the pressure in the FP cavity is controlled. The sensor was tested for operation above 1000°C. Strain-insensitive temperature measurement was demonstrated at ambient temperature for a strain range up to 3600 μe.

In order to reverse the malignant characteristics of hypopharyngeal cancer, the proteasome inhibitor MG132 was introduced into FaDu/T cells and the mechanisms underlying its effects were investigated. The multi-drug resistance (MDR) sensitivities of FaDu/T and FaDu/T-MG132 cancer cells to several chemotherapeutics were investigated by a 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) assay. Apoptosis was measured by staining cells with Annexin V and propidium iodide (PI) double staining. Reverse transcription-polymerase chain reaction and western blot analysis were conducted to detect mRNA and corresponding protein levels of the MDR- and apoptosis-related genes P-glycoprotein (P-gp), caspase-3, Bcl-2 and Bax. The nuclear protein of nuclear factor κ-light-chain-enhancer of activated B cells. (NF-κB) and p53 were also investigated via western blot analysis. Compared with FaDu/T cells, the drug resistance of FaDu/T + MG132 cells to cisplatin (DDP), 5-fluorouracil (5-FU), doxorubicin (Dox) and vincristine (VCR) decreased. With increased expression of caspase-3 and Bax and decreased expression of Bcl-2, the anti-apoptotic ability markedly decreased in FaDu/T + MG132 cells. P-gp and NF-κB significantly decreased; however, p53 increased in FaDu/T + MG132 cells. These results suggested that the proteasome inhibitor MG132 reversed the malignant characteristics of FaDu/T by enhancing apoptosis and inhibiting P-gp. MG132 was also able to inhibit the nuclear translocation of NF-κB and increase the expression of p53.

Based on the quantum-behaved particle swarm optimization (QPSO) algorithm and the discrete layer peeling (DLP) approach, we propose a scheme to design the right-angled triangular spectrum fiber Bragg gratings (RTS-FBGs). In this method, for a target reflectivity spectrum, the DLP approach is used to generate an appropriate initial guess of the complex coupling coefficients, and the QPSO technique is applied to optimize the initial complex coupling coefficients. For the QPSO method, the whole complex solution space can be searched for the coupling coefficients. Using the proposed method, single- and multi-channel RTS-FBGs are designed. Simulation results demonstrate that the edge of the right-angled triangular spectrums designed by our method is quite linear and the shape of the spectrum is also very consistent with the target spectrum, in contrast to those obtained by existing method. The RTS-FBGs can find potential applications in wavelength interrogation in optical sensor system.

A tunable multiwavelength erbium-doped fiber laser is proposed and experimentally studied. The intensity-dependent loss (IDL) in a nonlinear optical loop mirror is utilized for stable multiwavelength lasing output. The accurate switch operation, i.e., the lasing lines emerge/disappear one by one at the longer wavelength side of the initial one, is achieved by adjusting the intra-cavity loss using a variable attenuator. The effect of the intra-cavity loss on the lasing characteristics is theoretically analyzed. Numerical results confirm the experiment measurements and suggest that both the IDL and the gain spectrum, which vary with the intra-cavity loss, lead to the observed tunable lasing behavior.

The covariance matrix method is a simple method for solving the Zernike polynomial with the higher fitting precision. In this paper, it was used to analyze the several optical wave fronts of the fine polished aluminum disk surface captured by a Twyman-Green interferometer system. We had found that the PV (peak-to-valley) and rms (root-mean-square) values of the wave front aberration changes with changing the Zernike term and the expressions for the several optical wave fronts with the different sampling dots were wrong. By analyzing the relations among the condition number of the coefficients matrix, the Zernike term, and the number of the sampling dots, it was indicated that the number of the sampling dots had only reduced the fluctuation the PV and the rms value while the Zernike term increases, but did not change the case that the expressions for the wave front aberration were wrong when the Zernike term is larger than 14, especially when the number of the sampling dots is less. Such an analysis will be valuable in solving the Zernike polynomial for the wave front aberration analysis by using the covariance matrix method in optical testing.

Based on the mutated adaptive quantum-behaved particle swarm optimization (MAQPSO) algorithm and the discrete layer peeling (DLP) algorithm, we propose a method to design triangular-spectrum fiber Bragg gratings (TS-FBGs). In this method, the DLP algorithm is used to generate an appropriate initial range of the index modulation, and the MAQPSO technique is applied to optimize the index modulation within this range. The quantum-behaved particle swarm optimization algorithm with mutation operation can improve the search performance of this algorithm. We purposely use a linear weighting factor for the fitness value function in view of the linear edge triangular-spectrum. This dramatically accelerates the convergence in the numerical implementation. Using the proposed method, a 0.2 nm bandwidth TS-FBG is designed and the performance is shown to be better than previously reported results in the literature. Then, a 2.5 nm bandwidth TS-FBG is reconstructed; it is indicated that a short grating length can be used to realize the TS-FBG with chirp-free structure so that complex phase modulation is avoided in fabrication. Finally, a triple-channel TS-FBG with sampled-free structure is successfully designed and optimized. We also present an analysis on the tolerance of the design method over possible fabrication error.

The deduction of Zernike coefficients is usually influenced by the finite number of sampling dots on interferogram and their inherited measurement errors. In this paper, a simplified Gram–Schmidt method for solving the Zernike polynomial with the higher fitting precision is presented and used to analyze the wave front aberrations for the circle interference fringe of the fine polished aluminum disk surface captured by a Twyman-Green interferometer system. We find the stability of the Zernike coefficients changes with changing the Zernike term, which has lead to the wrong expression for the wave front aberration. By analyzing the condition number of the coefficients matrix and the fitting precision of the method, it is indicated that the instability can be avoided when the Zernike term is lower than 14. Such an analysis will be valuable in solving the Zernike polynomial for the wave front aberration analysis in optical testing.

We report an experimental demonstration of multiwavelength erbium-doped fiber laser with adjustable wavelength number exploiting a power-symmetric nonlinear optical loop mirror (NOLM). As the pump power increases from 53 mW to 410 mW, one–seven lasing line(s) at fixed wavelength around 1571 nm are obtained. A theoretical model describing the NOLM and the EDF is established to investigate the effect of the pump power on the lasing characteristics. Numerical results confirm the experiment measurements and indicate that it is the intensity-dependent loss of lasing beams generated in the NOLM that leads to such phenomena.

We report an experimental demonstration of muliwavelength erbium-doped fiber laser with adjustable wavelength number based on a power-symmetric nonlinear optical loop mirror (NOLM) in a linear cavity. The intensity-dependent loss (IDL) induced by the NOLM is used to suppress the mode competition and realize the stable multiwavelength oscillation. The controlling of the wavelength number is achieved by adjusting the strength of IDL, which is dependent on the pump power. As the pump power increases from 40 to 408 mW, 1–7 lasing line(s) at fixed wavelength around 1601 nm are obtained. The output power stability is also investigated. The most power fluctuation of single wavelength is less than 0.9 dB, when the wavelength number is increased from 1–7.

A new type of flat broadband Erbium-doped fiber (EDF) amplified spontaneous emission source is proposed and demonstrated. The intensity-dependent loss induced by a symmetric nonlinear optical loop mirror is used to flatten the spectrum and broaden the bandwidth. The 3 dB bandwidth over 50 nm has been obtained with 15 m EDF and 100 mW pump power based on the single-pass forward pump configuration. This spectrum flattening and broadening method is quite effective over a large range both in pump power and EDF length.

A model of multiwavelength erbium-doped fiber laser (MEFL), which takes into account the impact of fiber attenuation on the four-wave-mixing (FWM), is proposed. Using this model, we numerically study the output characteristics of the MEFL based on FWM in a dispersion shift fiber with two seeding light signals (TSLS) and experimentally verify these characteristics. The numerical and experimental results show that the number of output channels can be increased with the increase of the erbium-doped fiber pump power. In addition, by decreasing the spacing of TSLS and increasing the power of TSLS, the number of output channels can be increased. However, when the power of TSLS exceeds a critical value, the number of output channels decreases. The results by numerical simulation are consistent with experimental observations from the MEFL.

Intensity-based demodulation of extrinsic Fabry-Perot interferometric (EFPI) fiber-optic sensors requires the light wavelength to be on the quadrature point of the interferometric fringes for maximum sensitivity. In this Letter, we propose a novel and remote operating-point tuning method for EFPI fiber-optic sensors using microstructured fibers (MFs) and gas pressure. We demonstrated the method using a diaphragm-based EFPI sensor with a microstructured lead-in fiber. The holes in the MF were used as gas channels to remotely control the gas pressure inside the Fabry-Perot cavity. Because of the deformation of the diaphragm with gas pressure, the cavity length and consequently the operating point can be remotely tuned for maximum sensitivity. The proposed operating-point tuning method has the advantage of reduced complexity and cost compared to previously reported methods.